Four years ago today, this country suffered a terrible atrocity at the hands of terrorists: 52 people were killed and many more horribly injured. I stood at the dispatch box that day and spoke of the need to face down this barbarism. In the subsequent weeks and months, I was proud of the calm and just way that the ordinary British citizen dealt with this assault and of the comparative absence of people trying to make scapegoats of the ordinary, decent Muslim community. I was proud of the courage, sense of honour, tolerance and justice of our citizens at home.

I am afraid that I cannot be so complimentary about the actions of our government abroad. In the last year, there have been at least 15 cases of British citizens or British residents claiming to be tortured by foreign intelligence agencies with the knowledge, complicity and, in some cases, presence of British intelligence officers. One case – that of Binyam Mohammed – has been referred to the police by the attorney general, which implies that there is at least a prima facie case to answer. The most salient others include Moazzam Begg, Tariq Mahmoud, Salahuddin Amin and Rashid Rauf, all in Pakistan, Jamil Rahman in Bangladesh, Alam Ghafoor in United Arab Emirates, and Azhar Khan and others in Egypt.

For each case, the government have denied complicity, but at the same time fiercely defended the secrecy of their actions, making it impossible to put the full facts in the public domain, despite the clear public interest in doing so. Although the combined circumstantial evidence of complicity in all these cases is overwhelming, it has not so far been possible – because of the government's improper use of state secrecy to cover up the evidence – to establish absolutely clear sequences of cause and effect.

In the case I am about to describe, we can follow the entire chain of events from original suspicion, through active encouragement of the Pakistani authorities to arrest and through the subsequent collaboration between UK and Pakistani agencies. This is the case of Rangzieb Ahmed, a convicted terrorist, whose treatment I can describe in some detail.

As the house will realise, the account I am about to relay comes from several sources. I cannot properly give my sources, given the vindictive attitude of this government, particularly the Foreign Office, to whistleblowers. Indeed, in this case of Rangzieb Ahmed, the authorities were so paranoid that they threatened to arrest a journalist for reporting facts stated in open court. Nevertheless, although I am prevented from naming my sources, I can say that I am confident of these facts beyond reasonable doubt. I will not, of course, disclose any names, or anything that discloses intelligence agency techniques – other than torture – or other issues that threaten national security.

I should say that the individual whose case I am going to describe is not someone for whom I have any natural sympathy. He is a convicted – indeed, self-confessed – terrorist. So what I am talking about today is just as much about defending our own civilised standards as it is about deploring what was done to this man in the name of defending our country.

In 2005-06, Rangzieb Ahmed was a suspected terrorist who was kept under surveillance for about a year before leaving the country to go first to Dubai and on a subsequent trip to Pakistan. During that time, evidence was collected against him, on the basis of which he was later convicted. Let me repeat that point, as it is very important to my subsequent argument – during that time, evidence was collected, on the basis of which he was subsequently convicted.

Despite the authorities having that evidence, he was – astonishingly – not arrested but instead allowed to leave the country. To understand how odd this decision was, we should remember that this was only a year after the tragedy of 7/7, after which agencies were criticised for allowing terrorist suspects to leave the country to go to Pakistan. Since they knew he was leaving, since they knew where he was going, and since they had more than enough evidence to arrest him, allowing him to leave was clearly deliberate. That the authorities knew his itinerary is demonstrated by the fact that he was kept under surveillance when he was in Dubai. He later went on to Pakistan, where the Pakistani authorities were warned of his arrival by the British government. The British intelligence agencies wrote to their opposite numbers in Pakistan – the members of the directorate for inter-services intelligence – suggesting that they arrest him. I use the word "suggest" rather than "request" or "recommend" because of the peculiar language of the ISI's communication. No doubt the minister can confirm that for himself by asking to see the record.

We also know that the intelligence officer who wrote to the Pakistanis did so in full knowledge of the normal methods used by the ISI against terrorist suspects that it holds. That is unsurprising, as it is common public knowledge in Pakistan. The officer would therefore be aware that "suggesting" arrest was equivalent to "suggesting" torture.

Rangzieb Ahmed was arrested by the ISI on 20 August 2006. Once he was taken into custody in Pakistan by the ISI, the Manchester police and MI5 together created a list of questions to be put to him. MI5 arranged for those questions to be given to the ISI.

Rangzieb Ahmed was viciously tortured by the ISI. He says, among other things, that he was beaten with wooden staves the size of cricket stumps and whipped with a 3ft length of tyre rubber nailed to a wooden handle, and that three fingernails were removed from his left hand. There is a dispute between Ahmed and British intelligence officers about exactly when his fingernails were removed, but an independent pathologist employed by the Crown Prosecution Service confirmed that it happened during the period when he was in Pakistani custody.

Rangzieb was asked questions, under torture, about the UK by ISI officers. He claims that he saw "UK/Pakistan Secret" on the question list used by the ISI. That was presumably the list put together by the Manchester police and MI5. After about 13 days, he was visited by an officer from MI5 and another from MI6. He claims to have told them, during questioning, that he had been tortured. They deny that, but it is significant that they did not return for further interviews. By that stage, MI5 policy was not to return after any interview in which the subject claimed that he had been tortured. The British agents did not return, but Rangzieb was subsequently questioned by Americans.

Is it also an extraordinary, if sinister, coincidence that the Manchester police accessed Rangzieb Ahmed's medical records within days of the MI5/MI6 interview? Why would they do that if he was in perfect health?

Rangzieb Ahmed was kept in detention by the Pakistani authorities for a total of 13 months – first at the ISI centre, then at Rawalpindi and then at Adiyala jail – before being deported to the United Kingdom in September 2007. He was tried and convicted of terrorist offences in late 2008 – according to the prosecution, entirely on the basis of evidence obtained while he was under surveillance in the UK and Dubai in 2005-06. I cannot imagine a more obvious case of the outsourcing of torture, a more obvious case of "passive rendition".

Let me recap. Rangzieb Ahmed should have been arrested by the UK in 2006, but he was not. The authorities knew that he intended to travel to Pakistan, so they should have prevented that; instead, they suggested that the ISI arrest him. They knew that he would be tortured, and they arranged to construct a list of questions and supply it to the ISI.

The authorities know full well that this story is an evidential showcase for the policy of complicity in torture, should that evidence ever come out. One way in which the in camera veil of secrecy might be lifted would be a civil case by Mr Ahmed against the government for their complicity in torture. Part of that process would involve challenging the in-camera rulings and revealing the details of agency involvement. Just such a case was being considered by Mr Ahmed, and on 20 April this year he was visited in prison by his solicitor and a specialist legal adviser to discuss it.

Mr Ahmed tells us that a week later he was visited by an officer from MI5 and a policeman. That is the story told today on the front pages of the Daily Mail and the Guardian. During the course of their visit they said that they would like him to help in the fight against terror with information about extremism. This is perfectly proper.

However, the sinister part of this visit was an alleged request to drop his allegations of torture: if he did that, they could get his sentence cut and possibly give him some money. If this request to drop the torture case is true, it is frankly monstrous. It would at the very least be a criminal misuse of the powers and funds under the government's Contest strategy, and at worst a conspiracy to pervert the course of justice.

I would normally be disinclined to believe the word of a convicted terrorist. However, when he initially told his lawyer about it, he did not want to pursue the matter. Also, in common with many other criminals, after the scandal of the taping of the current minister of state, Department for Transport, the right honourable member for Tooting [Sadiq Khan], on a prison visit, he believes all these meetings are taped and he says this will back him up.

Given that belief, he is unlikely to have made an allegation that would be so easily proven wrong. I do not believe the conversation was taped, but it would have been videoed and this could be used to check his story. For reasons of policy and natural justice, it is imperative that the Crown Prosecution service investigates this allegation immediately, but that is not my principal concern today.

My questions to the minister are as follows. First, will he undertake to look at the in-camera court records and the records of the police and intelligence agencies so that he can confirm for his own satisfaction that my account of the handling of Rangzieb Ahmed pre-trial is correct? That process should take only a few days. Secondly, will he publish the current guidelines governing the agencies handling the suspected torture so that we can see whether the UK authorities broke those guidelines or whether it was the policy that was at fault? The prime minister has undertaken to publish the new guidelines, so if the minister cannot publish the current ones, can he explain why his approach is different to the prime minister's?

Thirdly, I believe, but cannot be certain to an evidential level, that the judge in the court case intimated that disciplinary action should be considered within the intelligence agencies. Was this done? If not, why not?

Finally, can the minister now announce a proper judicial inquiry into the allegations of UK complicity in torture, since it is now clear that there is not just circumstantial evidence but hard evidence in government records for ministers to read, if they had but eyes to see?

Let me conclude by saying that our handling of the subject of torture has, in my view, been completely wrong. The Americans have made a clean breast of their complicity, while explicitly not prosecuting the junior officers who were acting under instruction at a time of enormous duress and perceived threat after 9/11. We have done the opposite. As things stand, we are awaiting a police investigation that will presumably end in the prosecution of the frontline officers involved. At the same time, the government are fighting tooth and nail to use state secrecy to cover up crimes and political embarrassments to protect those who are probably the real villains in the piece – those who approved these policies in the first place.

The battle against terrorism is not just a fight for life; it is a battle of ideas and ideals. It is a battle between good and evil, between civilisation and barbarism. In that fight, we should never allow our standards to drop to those of our enemies. We cannot defend our civilisation by giving up the values of that civilisation. I hope the minister will today help me in ensuring that we find out what has gone wrong so we can return to defending those values once again.